1. Field of the Invention
The present invention relates generally to ink-jet technology and, more specifically, to an off axis ink delivery system.
2. Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions, incorporated herein by reference. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy sic! Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
Basically, it is known in thermal ink-jet printing to provide a printhead having an orifice plate in combination with heating elements. Thermal excitation of ink is used to eject droplets through tiny nozzles, or orifices, onto a print media. Dot matrix manipulation of the droplets provides alphanumeric character and graphics printing capabilities. Other ink-jetting mechanisms, such as by the use of piezoelectric transducers or wave propagation as ink droplet generators, are also well developed in the art.
The ink-jet pen itself may have a self-contained reservoir for storing ink and providing appropriate amounts of ink to the printhead during a printing cycle. These self-contained pens are also referred to in the art as print cartridges.
If a reusable pen rather than a print cartridge is employed in the hard copy apparatus, ink is generally supplied from a remote, off-axis (or off-board), ink reservoir to a relatively permanent pen body and printhead mechanism. Early ink-jet printers used off-axis reservoirs as demonstrated in U.S. Pat. No. 4,312,007 ((Winfield) assigned to the common assignee of the present invention and incorporated herein by reference). Moreover, it has been found that for some hard copy applications, such as large format plotting of engineering drawings and the like, there is a requirement for the use of much larger volumes of ink than can be contained within a reasonably sized, replaceable, print cartridge. Therefore, improved, relatively large, off-pen ink reservoir systems have also been developed more recently. As examples, refer to U.S. Pat. No. 4,831,389 (Chan) which shows a multicolor off-board ink supply system; U.S. Pat. No. 4,929,963 (Balazar) which demonstrates an ink delivery system for an ink-jet printer using a low pressure recirculating pumping system; and U.S. Pat. No. 4,968,998 (Allen) which teaches an ink-jet pen which is refillable at a service station (each assigned to the common assignee of the present invention and incorporated herein by reference).
While both print cartridges and ink-jet pens provide a reliable and efficient means of "jetting" droplets of ink from the printhead onto the print medium, the printheads generally require a mechanism to prevent the free flow of ink through the orifices when the printhead is not activated. Without such control, ink may leak, or "drool," onto the printing surface or into the printer mechanism. Such leaking ink may also build up and cake on the printhead itself, impairing proper operation. Complex pen service stations are often provided as part of the hard copy apparatus where printheads can be wiped or activated to "spit" away excess ink (known as priming). An exemplary service station is disclosed in U.S. Pat. No. 4,853,717 ((Harmon et al.) assigned to the common assignee of the present invention and incorporated herein by reference).
To alleviate this problem, many ink-jet printers supply ink from the reservoir to the printhead at a slight under pressure, lower than the ambient atmospheric pressure at the printhead (also referred to in the art as "back-pressure " or "negative pressure" operation). To be effective, pen back-pressure must be maintained consistently and predictably within a desired operating range. That is, the pen back-pressure must be large enough to prevent the unwanted free flow of ink through the orifices when the pen is not in use, yet at the same time small enough so that the printhead, when activated, can overcome the back-pressure and eject ink droplets in a consistent and predictable manner. This back-pressure will be affected by changes in either or both the ambient atmospheric and the pen's internal pressure conditions. Likewise, temperature variations may cause the ink and air within the ink-jet pen to contract or expand, also affecting the back-pressure. In addition to such operational variations, shipping print cartridges by air cargo often subjects them to extreme temperature and atmospheric pressure excursions. Therefore, these factors must be accounted for and a mechanism incorporated into an ink-jet pen to maintain the back-pressure within the predetermined, desirable operating range.
U.S. Pat. No. 4,771,295 ((Baker et al.) assigned to the common assignee of the present invention and incorporated herein by reference) shows a print cartridge employing an ink saturated foam where the capillary effect of the foam maintains the requisite back-pressure.
In order to increase print cartridge ink capacity, free-ink reservoirs have also been developed. In its basic aspect, a free-ink print cartridge apparatus includes a flexible bag that is spring loaded such that a predetermined design back-pressure is constantly provided during depletion of ink from the reservoir.
U.S. Pat. No. 4,509,062 (Low et al.), entitled "Ink Reservoir With Essentially Constant Negative Back Pressure" (assigned to the common assignee of the present invention and incorporated herein by reference) and U.S. Pat. No. 5,325,119 (Fong), entitled "Variable Rate Spring Ink Pressure Regulator for a Thermal Ink Jet Printer" (assigned to the common assignee of the present invention and incorporated herein by reference) teach particular mechanisms for dealing with back-pressure regulation in free-ink print cartridges. U.S. patent application Ser. Nos. 08/065,957 (Seccombe et al.) and 08/331,453 (Pawlowski Jr. et al.)(both assigned to the assignee of the present invention and incorporated herein by reference), disclose further inventions related to the spring bag concepts as employed in print cartridges.
In the quest for providing hard copy apparatus with the capability of higher print resolution (for example, 1200 dot per inch, near-photograph quality graphics) and for providing large format print graphics users with a reliable source of a greater volumes of ink than can be provided in reasonably sized, disposable print cartridges, there is a need for a system which employs a refillable, off-axis ink reservoir that is compatible with a relatively permanent pen and printhead that operates using the back-pressure concept.